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Week 7 Notes for CST8129
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-Ian! D. Allen - idallen@idallen.ca

*** Keep up on your readings (Course Outline: average 5 hours/week homework)

Remember - knowing how to find out an answer is more important than
    memorizing the answer.  Learn to fish!  RTFM!  (Read The Fine Manual)

Review of last week:
    wget -O, lynx -dump
    grep -A1 -e foo -e bar
    awk -F: '{print $1}' (compare usage with cut -f 1)
    cmp, find, groups, mail
    write, mesg
    tr -c -d -s
    gzip, gunzip, zcat, zless, zgrep, bzip2, bunzip2, bzcat, bzless, bzgrep
    script, col -b
    ln

Using the "ln" command to create more names for files:
    links_and_inodes.html     Hard links and Unix file system nodes (inodes)

    - names are separate from the things they name
    - names lead to inodes, which contain the permissions and data 
    - two or more names can lead to exactly the same inode
    - "ln" creates names for inodes, "rm" removes names
    - an inode with no names gets reclaimed ("deleted")
    - an empty directory has two names ("." is the second name!)
    - every sub-directory gives its parent a name of ".."
    - you can't create extra names for directories (because which name
      would ".." point to?  ".." has to be the unique parent.)

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This week:
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Shell conditional programming
    exit_status.txt     Return Code, Exit Status, test, if, and while

    - Unix commands return codes 0 to 255, with 0 meaning "success"
    - "exit 27" in a shell script will set the return code to 27
    - shell IF and WHILE statements check return codes
    - the leading "!" operator complements any return code
    - use the "test" command (aliased as "[") to do arithmetic
    - "test" will also test pathname RWX and other attributes

Sample shell scripts
    See the "Shell Scripts" section of the Course Notes for many
    sample shell scripts that demonstrate programming features.

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For next week (Week 8):
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Shell Variable and Command substitution:
    shell_variables.txt  Shell Variables you should know (including $* and $@)
    command_substitution.txt     Command Substitution - $(unix command)

More shell conditional logic:
    quick_tests.txt      Return Code, Exit Status, ||, &&, test, and if
    less_code.txt     Less Code is Better Code - stop cutting and pasting
    deep_nesting.txt     Avoiding deeply nested IF statements
    practiceTest2script.txt     Practice Script #1 Specifications
    practiceTest2script_answer.sh.txt     answer for above
    script_style.txt     Shell Script Programming Conventions and Style
    script_checklist.txt     Shell Script Checklist - things to verify

New commands:
    unix_command_list.txt     Basic Unix/Linux Command List